Boxcar averager

Thorn EMI 9235QB) near the phosphor screen to collect all of the ion signal as the probe laser was tuned over the 0(3Pj) Doppler profile at laser wavelengths of 226.23, 226.06 and 225.65 nm for j = 0, 1 and 2, respectively. The output of the photomultiplier was sent to a boxcar averager gated at the appropriate arrival time. The probe laser power was simultaneously measured with a photodiode in order to normalize the 0(3Pj) signal intensity for fluctuations in laser power. 

The reader may wish to extend the type of analysis shown in Fig. 3 by considering the effects of boxcar averaging. In this process, /(x) is convolved with a rect(x) function before sampling. Each sample then represents a uniformly weighted average. It is instructive to consider the effect of varying the number of samples used for the transform. In Chapter 9, Howard introduces the mathematics needed for practical application of the discrete Fourier transform. 

All TOF spectra are recorded with a 500-MHz digital oscilloscope (LeCroy) and averaged over several thousand laser shots. Boxcar averagers (Stanford Research) are used to integrate the signal of individual ion mass or electron eneigy peaks in the pump-probe experiments. The data are later corrected for laser fluctuations that are monitored by a photodiode. 

Solutions were flowed through a suprasil flat cell (0.1 mm thickness) at rates between 0.1 - S.O mL/min in order to minimize any interference from signals produced by secondary photolysis of products. Time-resolved polarization evolution profiles for the formation and relaxation of the polarized radicals were measured at a constant magnetic field and monitored by both a Hitachi 40 MHz digital oscilloscope and a Stanford Research Systems gated integrator/boxcar averager at 5 ns resolution, and both coupled to a 486 PC desk-top microcomputer for analysis. 

Experimental. The experimental set up consisted of a -pum-ped-dye laser (Molectron UV-14, DL-400), spatial filters to isolate the central part of the dye laser beam, a H2 02-Ar or N2 flame supported by a capillary burner with Ar or N2 sheath, and a fluorescence detection system at right angles (a JY-H-10 monochromator, a photomultiplier, and a PAR 162-164 boxcar averager). All measurements were taken 1 cm above the burner top the concentration of Ca, Sr, In, and Na was low ( 1 yg/ml). The fluorescence waveform was monitored with a 75 ps sampling head (PAR 163). The laser spectral bandwidth was also measured with a JY-HR-1000 monochromator (6AS < 0.1 ). 

The latter permits spectral scanning of the entire fluorescence spectrum using boxcar averaging. In Figure 15 is shown a comparison of the normal CH flame emission from an oxy-acetylene slot torch and the laser induced fluorescence spectrum. The CH was... 

Experiments are controlled by the PC, which is connected to the boxcar averager by a GPIB line. Boxcar parameters such as the number of data points to collect, the dwell time, and the number of scans to average, are set by using the PC. Data sets are then transferred from the boxcar averager to the PC for storage. The PC is connected by ethemet to a workstation computer, where data analysis is performed. 

Figure 7 An infrared spectrum and the results of applying a 5-point boxcar average, a 7-point average, and a 9-point average...

Back propagation, 150 Band limited signal, 28 Bayes theorem, 127 Boxcar averaging, 36... 

Fig. 119. Isotope-specific chromatograms of halogenated hydrocarbons (chlorobutane to chlorohexane) in methanol obtained by GC-MPT-TOFMS. Twin boxcar averagers are used for data collection, (a) Signal from 12C, (b) signal from 35CI. (Reprinted with permission from Ref. [76].)...

Fig. 127. Flame laser enhanced ionization spectrometry [670, 671]. (a) Flashlamp/dye laser, (b) high voltage, (c) trigger photodiode, (d) preamplifier, (e) pulse amplifier, (f) active filter, (g) boxcar averager, (h) chart recorder. (Reprinted with permission from Ref. [671]).

Curve 3. Here the acceptor concentration is 8.71 10 ° mole m A nitrogen pumped dye laser and boxcar averaging were employed for the fluorescence decay time measurements. 

Luminescence decay curves of both complexes excited with the 337 nm fundamental of the N2 laser at 77 K fit sufficiently well to a single exponential analysis. However, time resolution of the emission of Ir(ppy)2(bpy)+ via boxcar averaging techniques reveals a structured emission at long delay times... 

FIGURE 5-11 Effect of boxcar averaging (a) original data, (b) data after boxcar averaging. (From G. Dulaney. Anaf. Chem., 1975, 47, 27A. Figure 2, p. 27A. Copyright 1978 American Chemical Society.)... 

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